1. Field of the Invention
This invention is in the field of Direct Reaction Fuel Cells used to convert chemical energy in high-hydrogen-content fuels directly into electrical energy without burning the fuels for heat energy or reforming them for production of H2 and incorporating thick electrodes filled with catalyst, electrolyte cross-flow through the electrodes and means to provide relative motion between an electrode and an electrolyte between electrodes—including means for rotating an electrode (U.S. Class 429/67-69, Int. Class H01M 2/38), and means for allowing a fluid reactant or electrolyte to enter or leave the cell (U.S. Class 429/513, Int. Class H01M 8/04) so as to achieve accelerated chemical reaction rates promoted by Taylor Vortex Flows (TVF) and Circular Couette Flows (CCF).
2. Description of Related Art
A majority of current fuel cells employing aqueous chemistry typically incorporate electrodes having thicknesses of less than 150 microns (micrometers of μm) and proton exchange membranes (PEM) to retain electrolyte and to prevent crossover of fuel and oxidizer in the cells' electrolytes. These membranes also function as electrically-insulating separators between anode and cathode electrodes that are in contact with opposite faces of the membranes. A combination of the PEM and its electrodes is called a membrane electrode assembly (MEA).
PEM, such as NAFION® synthetic polymer, limit choices of electrolytes, temperatures and pressures of three-phase reduction/oxygen (redox) reactions of fuel-electrolyte-catalyst and oxidizer-electrolyte-catalyst that occur at interfaces of the membrane and its contiguous catalyst-bearing anode and cathode electrodes that form a membrane electrode assembly (MEA). In the case of NAFION polymer PEM, acidic electrolytes must be used and the operating temperature must not exceed 190° C. As a result, expensive catalysts (e.g., Platinum Group metals) are required to promote redox reactions while not corroding in electrolyte. Additionally, liquid fuels and oxidizers must be reformed to obtain gases and undesirable reactants (e.g., water) must be removed by a balance of plant (BOP).
The MEA electrode-PEM interfaces host gas diffusion layers where the redox reactions can occur. These layers are typically 10-50 microns (μm or micrometers) thick. The electrode faces adjacent the PEM contain catalyst particles (e.g., platinum, platinum alloys) to a depth of about 10-30 microns, which is approximately 1% of the thickness of a MEA. The thin gas diffusion layers contribute to limiting current densities to approximately 300 milliamperes per cm2 of electrode. Consequently, prior art fuel cells are uncompetitive in terms of cost-per-watt and power-per cm3. This is especially true for PEM Direct Reaction Fuel Cells.
My Direct Reaction Fuel Cells (DRFC), taught in Case D, and my Thick Electrode Direct Reaction Fuel Cells Utilizing Taylor Vortex Flows (TEDRFC), taught here, overcome temperature, proton transfer rate, oxygen reduction overvoltage, electrolyte storage and chemistry selection limitations of PEM fuel cells by eliminating any need for PEM and by providing a fuel cell containing means for creating Taylor Vortex Flows (TVF) in the electrolyte between its cathode and anode electrodes. TVF permits aqueous fuel cell operating temperatures to increase beyond the 190° C. PEM limit imposed by PEM and allows higher temperatures of 200° C. or more. Higher temperatures promote higher redox reaction rates and allow replacement of expensive Platinum Group metal catalysts with economical nickel and other low-cost catalysts. The elimination of PEM also removes restrictions on a selection of chemistries and permits use of either acid or alkali electrolytes, which offers more choices for handling and disposal of reaction byproducts (e.g., CO) or end products (e.g., H2O). TEDRFC of this invention provide further improvements in fuel cell current density and economics by providing new structures that facilitate use of electrolyte cross-flow through thick electrodes to achieve unprecedented current densities at lower capital cost.